Back to the issue of the third harmonic radiation let us choose initially
the interaction parameters as follow. At an intraband transitions the
interaction of a particle with the wave at the photon energies \(\hbar \omega >\mathcal {E}_{L}\)  [1]} characterizes by the known dimensionless
parameter \(\chi \) :
\(\chi =eE_{0}/(\omega \sqrt{m\hbar \omega }), \) 
